In OMA’s conversion of the Zollverein coal-washing plant, a glowing staircase channels visitors along the same route once taken by the coal. Photos by Thomas Mayer. Edited by Joseph Grima

Built in the ‘30s according to plans drawn up by two young German architects, Fritz Schupp and Martin Kremmer, as part of one of Europe’s largest coal-mining complexes, the Zollverein Kohlenwäsche building’s intended lifespan was of only 20 years – the amount of time it was expected to take to exhaust the underlying vein of coal. Instead, after extensive internal and external renovation by OMA, and after being granted UNESCO World Heritage protection, the site is now open to the public and houses a visitors’ centre, a major exhibition space and a restaurant. Floris Alkemade, partner-in-charge of the project at OMA, describes the building as a large machine: “The Kohlenwäsche wasn’t designed to be entered by people but by coal, so some parts were so crammed with machinery that it was impossible to access them. To make the building’s seven floors accessible we removed some of the coal-washing machinery and inserted a steel staircase that works as a vertical connector, winding its way down through the windlowless, bunker-like vertical space that used to be used for storing the coal. Visible signs of our intervention on the rest of the building are very limited, especially on the exterior: the only things we added are the escalator and a glass meeting room on the roof. Paradoxically, the way the building works hasn’t changed that much – just as coal used to be taken to the top of the building by conveyor belts and then moved downwards as it went through the purification process, today visitors are elevated to the top floor by the escalator, and from there they are led downwards from floor to floor by the staircase.”

Being the most visible sign of the building’s conversion, OMA strove to make the escalator a clearly identifiable symbol of its new use. Using technology developed with Kruppe and previously employed in Seattle Public Library, it was decided to colour the treads and sidepanels orange; the result, especially at night-time, is reminiscent of a river of molten steel. With a span of 24 metres, it is the longest free-standing escalator in Europe. The interior staircase is fabricated in unpainted steel; the illusion that it is coloured bright orange is created by the tinted strip lights set into the side-panels.